With one Toronto man estimating he has up to 1,000 half-siblings, some fertility-treatment experts are calling on Canada to legally restrict how many children can be born from a single donor’s semen.

The growing families of donor offspring could cause unusual spread of genetic malformations, raise the risk of inadvertent incest between biological brothers and sisters and prove emotionally taxing to the children, critics say.

Although medical groups and others already recommend restrictions in the number of pregnancies per donor, legislation is needed to ensure sperm banks and their suppliers follow the proper limits, said Juliet Guichon, a bio-ethics professor at the Unviersity of Calgary.

“It [self regulation] is not working,” said Prof. Guichon. “There’s no incentive. It’s the market economy: why would you limit business?”

Various reports on the infertility industry, including the 1993 federal Royal commission on new reproductive technology and an earlier B.C. commission, have actually been recommending limits of as few as six pregnancies per donor for the last 30 years, she said.

Britain, some Australian states, New Zealand, the Netherlands and a handful of other European countries already have laws that restrict the number of children per donor, Prof. Guichon noted.

The issue came to the fore again this week, however, with reports from the U.S. — which has no legislated limits — that one donor there has 150 offspring. The genetic siblings have been catalogued on an unofficial but widely used American web site — the Donor Sibling Registry — that brings together such relatives, sometimes based on the number assigned to the donor by his sperm bank.

The Colorado-based registry’s director says another group of 75 offspring includes several Canadians. About 95% of sperm used in artificial insemination and in-vitro fertilization treatments here actually comes from the States.

Barry Stevens, a Toronto filmmaker, said he was born in the U.K. in 1952 with sperm from a donor who supplied his semen over about three decades, and probably produced 500 to 1,000 children, now spread through Britian, Canada and other countries.

“There should be limits, because if some offspring want to find their relatives, and want to meet their donor … it’s kind of daunting when it’s in the hundreds,” he said. “For some, it becomes kind of creepy and freaky.”

The fertility industry has restricted its practices considerably since the start of artificial-insemination around the middle of the last century, but critics say the lack of regulation or monitoring of what happens to donor sperm means the real-life practice is still largely unknown.

At ReproMed, which runs Canada’s only sperm bank, administrators do impose restrictions, said Dr. Alfonso Del Vaille, its director. Donors are limited to three live births per 100,000 population in a given geographic area, though that could mean as many as 75 offspring in a city the size of Toronto.

Dr. Del Vaille said he would support legislated limits, so long as they are based on good science.

The chief concern stemming from large donor families is the risk that half-siblings unknowingly enter sexual relationships, upping the risk of birth defects in any resulting children.

Mr. Stevens said he knows of donor offspring who have married or had sex with half siblings, and said the chance of that happening is greater than it might seem. He said he has talked to a U.S. donor who moved to Toronto and ended up by sheer coincidence living next door to a lesbian couple whose children were born with the use of his sperm.

Experts also worry about the possibility that a genetic flaw, which would be passed on to only a couple of children in a natural family, could be spread to dozens more through sperm or egg donation.

And there is also the less tangible effect of a child learning that their direct biological family extends far and wide. Wendy Kramer, the donor-registry’s director, recalls one mother who came to the web site anxious to find one or two genetic siblings to her daughter, an only child, only to discover the donor had sired 18 offspring.

“The mother was upset: ‘Oh, my God, I didn’t expect this … How do I create a connection with 18 families?’ ”

Even some of those in the fertility industry itself say there is a need to legislate limits, though doing so would likely further restrict the supply of donor sperm. “It’s one of those big picture areas that as a society and as a culture we really need to sit down and think about what we are doing,” said Roger Pierson, a University of Saskatchewan fertility expert and spokesman for the Canadian Fertility and Andrology Society.

Which government would enact such laws in Canada is another question, though, since the federal Assisted Human Reproduction Act, designed to govern such matters, was declared mostly unconstitutional by the Supreme Court last year.

It could be that the provinces would have to band together and bring in legislation jointly, said Ms. Guichon.

Other experts say the federal government, which still does regulate the importation of sperm, could impose rules allowing only sperm that has produced a limited number of offspring to be brought in to the country from elsewhere.

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